Systems and methods for using a satellite positioning system to detect moved wlan access points

ABSTRACT

The disclosed subject matter generally relates to hybrid positioning systems and methods and, more specifically, systems and methods of detecting moved WLAN assess points using a wireless local area network based positioning system (WLAN-PS) and a satellite-based positioning system (SPS) with at least two satellites measurement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/504,373, filed Jul. 16, 2009, and entitled “Systems and Methods forUsing a Satellite Positioning System to Detect Moved WLAN AccessPoints”, now U.S. Pat. No. (TBA), incorporated by reference herein.

This application is related to the following U.S. patent applications:

-   -   U.S. patent application Ser. No. 12/504,379, filed Jul. 16,        2009, and entitled “Methods and Systems for Determining Location        Using a Hybrid Satellite and WLAN Positioning System by        Selecting the Best SPS Measurements”;    -   U.S. patent application Ser. No. TBA, filed Aug. 17, 2011, Atty.        Docket No. 2000319.158 US3, and entitled “Systems and Methods        for Using a Satellite Positioning System to Detect Moved WLAN        Access Points”;    -   U.S. patent application Ser. No. TBA, filed Aug. 17, 2011, Atty.        Docket No. 2000319.158 US4, and entitled “Systems and Methods        for Using a Satellite Positioning System to Detect Moved WLAN        Access Points”; and    -   U.S. patent application Ser. No. TBA, filed Aug. 17, 2011, Atty.        Docket No. 2000319.158 US5, and entitled “Systems and Methods        for Using a Satellite Positioning System to Detect Moved WLAN        Access Points”.

BACKGROUND

1. Field

The disclosed subject matter generally relates to hybrid positioningsystems and, more specifically, to detecting movement of WiFi accesspoints using information from two or more satellites in an integratedwireless local area network based positioning system (WLAN-PS) andsatellite-based positioning system (SPS).

2. Description of Related Art

In recent years the number of mobile computing devices has increaseddramatically, creating the need for more advanced mobile and wirelessservices. Mobile email, walkie-talkie services, multi-player gaming andcall-following are examples of how new applications are emerging formobile devices. In addition, users are beginning to demand/seekapplications that not only utilize their current location but also sharethat location information with others. Parents wish to keep track oftheir children, supervisors need to track the locations of the company'sdelivery vehicles, and a business traveler looks to find the nearestpharmacy to pick up a prescription. All of these examples require anindividual to know his own current location or the location of someoneelse. To date, we all rely on asking for directions, calling someone toask their whereabouts or having workers check-in from time to time toreport their positions.

Location-based services are an emerging area of mobile applications thatleverage the ability of new devices to calculate their currentgeographic positions and report them to a user or to a service. Examplesof these services range from obtaining local weather, traffic updatesand driving directions to child trackers, buddy finders and urbanconcierge services. These new location-sensitive devices rely on avariety of technologies that all use the same general concept. Bymeasuring radio signals originating from known reference points, thesedevices can mathematically calculate the user's position relative tothese reference points. Each of these approaches has its strengths andweaknesses depending upon the nature of the signals and measurements,and the positioning algorithms employed.

The Navstar Global Positioning System (GPS) operated by the USGovernment leverages about two-dozen orbiting satellites in medium-earthorbits as reference points. A user equipped with a GPS receiver canestimate his three-dimensional position (latitude, longitude, andaltitude) anywhere at any time within several meters of the truelocation as long as the receiver can see enough of the sky to have fouror more satellites “in view.” Cellular carriers have used signalsoriginating from and received at cell towers to determine a user's or amobile device's location. Assisted GPS (AGPS) is another model thatcombines both GPS and cellular tower techniques to estimate thelocations of mobile users who may be indoors and must cope withattenuation of GPS signals on account of sky blockage. In this model,the cellular network attempts to help a GPS receiver improve its signalreception by transmitting information about the satellite positions,their clock offsets, a precise estimate of the current time, and a roughlocation of the user based on the location of cell towers. Nodistinction is made in what follows between GPS and AGPS.

All positioning systems using satellites as reference points arereferred to herein as Satellite-based Positioning System (SPS). WhileGPS is the only operational SPS at this writing, other systems are underdevelopment or in planning A Russian system called GLONASS and aEuropean system called Galileo may become operational in the next fewyears. All such systems are referred to herein as SPS. GPS, GLONASS andGalileo are all based on the same basic idea of trilateration, i.e.,estimating a position on the basis of measurements of ranges to thesatellites whose positions are known. In each case, the satellitestransmit the values of certain parameters which allow the receiver tocompute the satellite position at a specific instant. The ranges tosatellites from a receiver are measured in terms of the transit times ofthe signals. These range measurements can contain a common bias due tothe lack of synchronization between the satellite and receiver (userdevice) clocks, and are referred to as pseudoranges. The lack ofsynchronization between the satellite clock and the receiver (userdevice) clock can result in a difference between the receiver clock andthe satellite clock, which is referred to as internal SPS receiver clockbias or receiver clock bias, here. In order to estimate a threedimensional position there is a need for four satellites to estimatereceiver clock bias along with three dimensional measurements.Additional measurements from each satellite correspond to pseudorangerates in the form of Doppler frequency. References below to raw SPSmeasurements are intended generally to mean pseudoranges and Dopplerfrequency measurements. References to SPS data are intended generally tomean data broadcast by the satellites. References to an SPS equation areintended to mean a mathematical equation relating the measurements anddata from a satellite to the position and velocity of an SPS receiver.

WLAN-based positioning is a technology which uses WLAN access points todetermine the location of mobile users. Metro-wide WLAN-basedpositioning systems have been explored by several research labs. Themost important research efforts in this area have been conducted by thePlaceLab (www.placelab.com, a project sponsored by Microsoft and Intel);the University of California, San Diego ActiveCampus project(ActiveCampus—Sustaining Educational Communities through MobileTechnology, technical report #CS2002-0714); and the MIT campus-widelocation system. There is only one commercial metropolitan WLAN-basedpositioning system in the market at the time of this writing, and it isreferred to herein as the WPS (WiFi positioning system) product ofSkyhook Wireless, Inc (www.skyhookwireless.com).

FIG. 1 depicts a conventional WLAN-based positioning system based onWiFi signals. The positioning system includes positioning software 103that resides on a mobile or user device 101. Throughout a particulartarget geographical area, there are a plurality of fixed wireless accesspoints 102 that transmit information using control/common channelsignals. The device 101 monitors these transmissions. Each access pointcontains a unique hardware identifier known as a MAC address. The clientpositioning software 103 receives transmissions from the 802.11 accesspoints in its range and calculates the geographic location of thecomputing device using the characteristics of the radio signals. Thosecharacteristics include the MAC addresses, the unique identifiers of the802.11 access points, the Time of Arrival (TOA) of the signals, and thesignal strength at the client device 101. The client software 103compares the observed 802.11 access points with those in its referencedatabase 104 of access points. This reference database 104 may or maynot reside in the device 101. The reference database 104 contains thecalculated geographic locations and power profiles of all access pointsthe system has collected. A power profile may be generated from acollection of measurements of the signal power or signal TOA at variouslocations. Using these known locations or power profiles, the clientsoftware 103 calculates the position of the user device 101 relative tothe known positions of the access points 102 and determines the device's101 absolute geographic coordinates in the form of latitude andlongitude or latitude, longitude and altitude. These readings then canbe fed to location-based applications such as friend finders, localsearch web sites, fleet management systems, and an E911 service.

In the discussion herein, raw WLAN measurements from an access point aregenerally intended to mean received signal strength (RSS) and/or timesof arrival (TOAs) and/or time differences of arrival (TDOAs). Referencesto data are generally intended to mean the MAC address, one or morerecord(s) of it, one or more power profile(s), and other attributesbased on previous measurements of that access point. References to aWLAN-PS equation are intended to mean a mathematical equation relatingthe WLAN-PS measurements and data to the location of the mobile device.

A WLAN-based positioning system can be used indoors or outdoors. Theonly requirement is presence of WLAN access points in the vicinity ofthe user. The WLAN-based position systems can be leveraged usingexisting off-the-shelf WLAN cards without any modification other than toemploy logic to estimate position.

FIG. 2 illustrates a conventional way of integrating WLAN-PS and SPS,which consists of a WLAN-PS 201 and a SPS 206, and a location combininglogic 210.

WLAN-PS 201 and SPS 206 are stand-alone systems and each can operateindependently of the other system. Thus, the result of each system canbe calculated independent of the other system. The estimated locationalong with the expected error estimation of each system can be fed tothe location combining logic 210. The expected error estimation also isreferred to as HPE (horizontal positioning error) herein. The nominalrate of location update of SPS 206 and WLAN-PS 201 is once per second.The location combining logic 210 combines location estimates calculatedin the same second by both systems.

WLAN-PS 201 is a conventional system which estimates the location of amobile device by using WLAN access points. WLAN-PS 201 can include ascanner of WLAN APs 202, a select WLAN APs device 203, a trilaterationdevice 204, and HPE estimation device 205.

WLAN Scanner 202 detects WLAN APs surrounding the mobile device bydetecting the received power (RSS, received signal strength) and/or timeof arrival (TOA) of the signal. Different methods can be used to detectWLAN APs including active scanning, passive scanning or combination ofpassive and active scanning.

The select WLAN APs device 203 selects the best set of WLAN APs toestimate the location of the mobile device. For example, if ten WLAN APsare detected and one AP is located in Chicago and the other nine arelocated in Boston, without any other information, the Boston APs areselected. This is an indication that Chicago AP has been moved toBoston. Please see U.S. patent application Ser. No. 11/359,154 as filedFeb. 22, 2006 and entitled “Continuous Data Optimization of Moved AccessPoints in Positioning Systems,” the entire contents of which are herebyincorporated by reference. In the conventional system the best set ofWLAN APs can be selected based on geographical distribution of WLAN APsin addition to corresponding parameters of WLAN APs, including receivedsignal strength, signal to noise ratio, and the probability of beingmoved.

The trilateration device 204 can use WLAN APs and their correspondingmeasurements and characteristics to estimate the location of the mobiledevice. Received signal strength or TOA measurements from the WLAN APcan be used to estimate the distance of the mobile device to the WLANAP. The aggregation of distance estimates from different WLAN APs withknown location of the APs can be used to calculate location of themobile device. Trilateration device 204 also can use a method which iscalled nearest neighbor, in which a location with a power profilesimilar or closest to the power reading of the mobile device is reportedas the final location of the mobile device. The power profile of eachWLAN AP or entire coverage area can be found in the calibration phase ofthe system by detailed survey of the coverage area.

HPE estimation device 205 is the module which estimates the expectederror of the position estimate of the mobile device. The HPE orHorizontal Positioning Error is calculated based on previously scannedAPs and their characteristics and also on characteristics of thereceived signal as was discussed in co-pending Skyhook Wirelessapplication Ser. No. 11/625,450 entitled “System and Method forEstimating Positioning Error Within a WLAN Based Positioning System,”the entire disclosure of which is hereby incorporated by reference.

The SPS system 206 consists of a satellite signal receiver andmeasurement device 207, trilateration device 208, and the SPS HPEestimation device 209.

The satellite signal receiver and measurement device 207 receivessignals from the satellites in view of the device, decodes the receivedsignal, and measures the satellite parameters from each satellite. Themeasurements can include pseudorange, carrier frequency, and Dopplerfrequency.

The trilateration device 208 uses measurements from at least foursatellites and location of the satellites in view to estimate locationof the user device, velocity, and direction of travel of the mobiledevice.

HPE estimation device 209 estimates the expected error of the estimatedlocation. The HPE estimation device 209 is conventional and calculatesexpected error based on geometry of the satellites and signal quality ofthe received signal from satellites, for example, DOP (dilution ofprecision), and C/N (carrier to noise ratio).

Location combining logic 210 receives location and HPE estimatescalculated for almost the same second from WLAN-PS 201 and SPS 206. Inother words, measurements and estimations which are made at the sametime are compared and combined. Practically, measurements andestimations within one second can be considered the same time. Thelocation combining logic 210 of the user device reports one estimatedlocation by selecting one of them or linearly combining them. Forexample, location combining logic might select one of the estimatedlocations provided by WLAN-PS 201 or SPS 206 based on reported expectederror, HPE, or it might report weighted average of estimated locationsby both systems according to the HPE.

SUMMARY

The disclosed subject matter generally relates to hybrid positioningsystems and methods and, more specifically, systems and methods fordetecting moved WLAN assess points using a wireless local area networkbased positioning system (WLAN-PS) and a satellite-based positioningsystem (SPS) with at least two satellites measurement.

In one aspect the disclosed subject matter relates to a method of usinga WLAN and satellite enabled device to detect WLAN access points (APs)that have moved, the method can include, detecting WLAN APs in range ofthe WLAN and satellite enabled device, accessing a reference database toobtain a reference location of each WLAN AP, obtaining satellitemeasurements from at least two satellites to provide a plurality ofpossible SPS location solutions of the device, calculating a distancebetween each reference WLAN AP location and the possible SPS locationsolutions, and if the distance between the reference WLAN AP locationand the SPS location solutions is far, determining that the WLAN APlocation and/or other associated data to the WLAN AP in the referencedatabase is not correct.

In some embodiments, the method can include notifying the referencedatabase that the WLAN AP location is not correct.

In some embodiments, the method can include updating the referencedatabase's location for the WLAN AP.

In some embodiments, the possible SPS location solutions of the devicecan include a region of possible location solutions for the device.

In some embodiments, the reference WLAN AP location is far from the SPSlocations solutions if the distance is an order of magnitude above thecoverage area of the AP.

In some embodiments, the method can include measuring a consistencybetween the satellite measurements and the WLAN AP reference location.

In some embodiments, the WLAN AP reference location consistency with thesatellite information can be measured by applying each of the WLAN APreference locations to the satellite measurements and calculating aninternal SPS receiver clock bias for each WLAN AP reference location.

In some embodiments, a consistency of the internal SPS receiver clockbias for each of the WLAN AP locations can be used as an indication ofdistance between the WLAN AP location and the possible SPS locationsolutions of the device.

In some embodiments, calculating the consistency of the internal SPSreceiver clock bias for each WLAN AP reference location can includecalculating the standard deviation or the mean square error of theinternal SPS receiver clock bias.

In some embodiments, the method includes calculating an internal SPSreceiver clock bias by considering the WLAN AP reference location as aninitial position.

In one aspect the disclosed subject matter relates to a system fordetermining the location of a WLAN and satellite enabled device todetect moved WLAN access points (APs) can include a hybrid positioningmodule, a WLAN module for receiving information from one or more WLANaccess points, a satellite positioning module for providing a pluralityof possible device locations of the device based on satelliteinformation from at least two different satellites, a reference databasefor storing reference locations for each WLAN AP, and logic contained inthe positioning module for calculating a distance between each referenceWLAN AP location and the possible SPS location solutions and if thedistance between the reference WLAN AP location and the SPS locationsolutions is far, determining that the reference WLAN AP location isincorrect.

In some embodiments, the possible SPS location solutions of the devicecan include a region of possible location solutions for the device.

In some embodiments, the reference WLAN AP location is far from the SPSlocations solutions if the distance is an order of magnitude above thecoverage area of the AP.

In some embodiments, the logic can be configured to measure aconsistency between the satellite measurements and the WLAN AP referencelocation.

In some embodiments, the WLAN AP reference location consistency with thesatellite information can be measured by applying each of the WLAN APreference locations to the satellite measurements and calculating aninternal SPS receiver clock bias for each WLAN AP reference location.

In some embodiments, a consistency of the internal SPS receiver clockbias for each of the WLAN AP locations can be used as an indication ofdistance between the WLAN AP location and the possible SPS locationsolutions of the device.

In some embodiments, calculating the consistency of the internal SPSreceiver clock bias for each WLAN AP reference location can includecalculating the standard deviation or the mean square error of theinternal SPS receiver clock bias.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of various embodiments of the presentinvention, reference is now made to the following descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 illustrates a high-level architecture of a WLAN positing system;

FIG. 2 illustrates a system for a conventional way of integratingWLAN-PS and SPS;

FIG. 3 illustrates a system of integrated WLAN-PS and SPS system, inwhich the WLAN-PS detects WLAN access point (AP) movement by using SPSinformation, according to one or more embodiments of the disclosedsubject matter;

FIG. 4A illustrates the use of an integrated WLAN-PS and SPS system todetect WLAN access point (AP) movement, according to one or moreembodiments of the disclosed subject matter;

FIG. 4B illustrates the use of an integrated WLAN-PS and SPS system todetect WLAN access point (AP) movement, according to one or moreembodiments of the disclosed subject matter;

FIG. 5 illustrates a system for selecting the best set of measurementsfrom the collective measurements from satellites and WLAN APs, accordingto one or more embodiments of the disclosed subject matter;

FIG. 6 illustrates a system for selecting the best set of satellitemeasurements by using WLAN-PS, according to one or more embodiments ofthe disclosed subject matter; and

FIG. 7 illustrates an integrated WLAN-PS and SPS system, in which WLANAPs and SPS measurements are combined and the best set of measurementsbetween both systems are selected to estimate location of the mobiledevice, according to one or more embodiments of the disclosed subjectmatter.

DETAILED DESCRIPTION

Embodiments of the disclosure provide systems and methods for detectingmoved WLAN access points in an integrated or hybrid system of WLAN-basedpositioning system (WLAN-PS) and satellite-based positioning system(SPS) by using received signals from two or more satellites. TheWLAN-based positioning system relies on knowing the location of WLANaccess points and using them as reference points to estimate a locationof a mobile device. The mobile device is equipped with both a satellitereceiver and a WLAN receiver for receiving signals from satellite andWLAN access points (APs), respectively. If a WLAN access point moves andthe WLAN-based positioning system still uses the old location of theWLAN access point as the reference location, then the WLAN-PS willreport a location corresponding to the old location of the WLAN accesspoint, which might be far from its current location. In an integratedsystem of a WLAN-based positioning system and a satellite-basedpositioning system, moved WLAN access points are detected by using anSPS position estimate or by using two or more satellites with no SPSposition estimate. In situations where it has been determined that oneor more WLAN APs have moved from the location logged in the WLAN-PSdatabase, the new AP location can be determined and the WLAN-PS APposition database can be updated accordingly.

In the case that an SPS location estimate does not exist, butmeasurements from two satellites are acquired, the first step to detectWLAN AP movement can be to consider the location of the WLAN AP as aninitial location estimate of the mobile device. The location of the WLANAP can be determined by accessing the known or reference location of theWLAN AP in a reference database. The reference database containsreference locations of a plurality of WLAN APs. These locations may havebeen determined through numerous methods including performing a sitesurvey of the coverage area, logging location of WLAN APs at the time ofinstallation, or estimating the location of WLAN APs from receivedsignal strength (RSS) at some known locations in the coverage area. WLANAPs are uniquely identified using their MAC (medium access control)address which is uniquely assigned to each WLAN AP by the manufacturer.

Then, the clock bias of a SPS receiver in the mobile device can bedetermined based on the measurements from all the acquired satellites inview of the mobile device and the location of the AP. Because themeasurements from all the acquired satellites are made at substantiallythe same time, the same clock bias at the receiver of SPS can be usedfor all the measurements. If it is assumed that N number of satellitesare acquired and satellite parameters are as follows:

Pseudo-range: P

Ionospheric delay: I

Tropospheric delay: T

Location of satellite Xs, Ys, and Zs

and WLAN AP location is shown as X, Y, and Z

the clock bias of SPS receiver is found as follows:

Ci=P _(i)−√{square root over ((Xs _(i) −X)²+(Ys _(i) −Y)²+(Zs _(i)−Z)²)}{square root over ((Xs _(i) −X)²+(Ys _(i) −Y)²+(Zs _(i)−Z)²)}{square root over ((Xs _(i) −X)²+(Ys _(i) −Y)²+(Zs _(i) −Z)²)}−I_(i) −T _(i); 0≦i≦N

Therefore, if the AP location is the exact location of the mobile deviceand that location is applied to the above satellite measurements, theexact same clock bias will be found from all the N satellite equations.Thus, the consistency between the calculated clock biases based on eachsatellite measurement can be used as an indication of a discrepancy ordistance between the WLAN-PS initial location (WLAN AP location in thisexample) and the satellite measurements (which indicate the actuallocation of the mobile device). If the inconsistency between the clockbias numbers found from the SPS equations for each satellite afterapplying the WLAN AP location is large, it is concluded that the WLAN APhas moved. In some cases, the new location of WLAN AP may not be able tobe determined if there is no estimate for the location of the mobiledevice. Any statistical method to measure the spread of clock biasmeasurements can be used here. For example, the spread can be measuredby finding standard deviation of clock bias values or mean square error(MSE) as follows:

$\overset{\_}{C} = \frac{\sum\limits_{i = 1}^{N}C_{i}}{N}$${M\; S\; E} = \frac{\sum\limits_{i = 1}^{N}\left( {C_{i} - \overset{\_}{C}} \right)^{2}}{N}$

An example of large inconsistency or a far distance can be in the orderof hundreds of meters in case of standard deviation or if the distanceis an order of magnitude larger than the coverage area of the WLAN AP.For example, if the coverage area of the WLAN AP is 100 meters, a fardistance would be on the order of 1,000 meters. However, if the coveragearea of the WLAN AP is 10 meters, a large distance would be 100 meters.Therefore, the determination of whether or not a distance is far dependson the coverage area of the access points being used for the locationdetermination.

When a SPS location estimate is available, the difference between thelocation of WLAN APs and the SPS location estimate can be used to detectWLAN AP movement or confirm the general location of detected WLAN APs bythe mobile device.

If the difference between location of a WLAN AP and SPS locationestimate is large (WLAN AP reference location and SPS location estimateare far from each other), i.e., an order of magnitude higher thanexpected coverage of the WLAN AP, it can be concluded that the WLAN APhas moved. The coverage of the WLAN AP might be known, for example, bysurveying the area. If the coverage of a WLAN AP is not known, a nominalcoverage can be considered. A nominal or typical coverage area of a WLANAP can be found statistically by measuring the coverage areas for many(e.g. thousands) of WLAN APs. Nominal coverage areas can be defined as asphere with the WLAN AP as the center of the sphere, having a radiusbetween 100 m and 250 m.

If WLAN AP movement is detected, the new location in which the WLAN APwas detected can be used to correct and update the location of the WLANAP in the reference database.

This process of detecting WLAN AP movement can be applied to everydetected WLAN AP.

FIG. 3 illustrates a block diagram of the hybrid system of a WLAN-PS 301and a SPS 306, in which an SPS location estimate 312 and also raw SPSmeasurements 311 can be provided to the WLAN-PS to detect AP movement.

The SPS 306 is an off-the-shelf, conventional satellite positioningdevice which consists of the same devices as SPS 206 in FIG. 2, with theaddition of the raw measurement output 311 and the SPS location estimateoutput 312. The satellite receiver and measurement device 207 is acomponent of every conventional SPS receiver 306, and raw SPSmeasurements are an essential part of the SPS measurement. However, herethe raw SPS measurements are used outside the SPS 306, as is shown bySPS measurement output 311. Not all the commercial SPS receivers exposethe raw SPS measurements to devices outside SPS 306. For example, StarIII GPS manufactured by SiRF Technology, Inc. (San Jose, Calif.),provides raw SPS measurements as part of its standard interface.However, there are some other GPS receivers that do not provide suchmeasurements. For the SPS receivers that do not expose raw SPSmeasurements as part of their standard interface, the SPS receiver 306can be modified to permit access to the raw SPS measurements.

The WLAN-PS 301 functions in a similar manner as the WLAN-PS 201 shownin FIG. 2 except that WLAN AP selection device 303 is configured toreceive raw SPS measurements 311 and an SPS location estimate 312 whenthey are available. The integration of the raw SPS measurement 311 andthe SPS location estimate 312 with WLAN-PS 301 changes the design ofWLAN APs selection device 303. The WLAN-PS 301 can take advantage of theraw SPS measurements when at least two satellites are acquired evenwithout any fix or solution from the SPS 306.

WLAN APs selection device 303 receives the SPS location estimate 312 orraw SPS measurements 311, if they are available, and measures thedistance between the location of each WLAN AP and the SPS locationestimate or possible satellite locations solutions derived from raw SPSmeasurements. WLAN APs, which are not consistent with SPS locationestimate or solutions, are declared as moved and removed from the listof APs to locate the mobile device. The WLAN APs, which are detected asmoved by WLAN AP selection device 303, are flagged and logged as beingmoved to a new location in the reference database.

FIG. 4A illustrates an integrated WLAN-PS 401 and SPS positioning system406. The WLAN-PS 401 uses WLAN APs 402 to estimate the location of themobile device and the expected error in that location estimation 405.The expected error of the location estimate refers to the generalgeographical region 405. However, in this example, the SPS 406 usesacquired satellites 404 to report a location 403 which is far from the405 region. Therefore, it is concluded that the WLAN APs 402 were movedto a new area close to the location 403 reported by SPS 406.

FIG. 4B illustrates an integrated WLAN-PS 401-2 and SPS 406-2, whenmeasurements from satellites 404-2 do not result in a location estimateof the mobile device, but at least two satellites 404-2 are acquired.The WLAN-PS 401-2 uses WLAN APs 402-2 to estimate the location of themobile device. Considering the expected error of the location estimateof the WLAN-PS, there will be a general geographical region 405-2 of theWLAN-PS location estimate. Acquired satellites 404-2 refer to a set ofpossible locations for the mobile device 403-2. If the WLAN-PS generalarea 405-2 is far from the SPS possible location estimates for themobile device 403-2, it is concluded that the WLAN APs 402-2 were movedto the new area close to the general area reported by SPS 403-2.

Another embodiment provides a method and system to integrate WLAN-PS andSPS by selecting the best set of raw measurements between both systemsand/or rejecting low quality measurements from either system afterconsidering estimates from both systems. Measurements can refer to theaggregate of WLAN-PS and SPS measurements. Considering the aggregatedset of WLAN and SPS measurements, the first step is to determine whetherthe measurements from WLAN APs and the satellite measurements form morethan one cluster.

Each cluster of only satellite measurements includes of a minimum ofthree satellites. In the case of less than four satellite measurementsin a cluster, a cluster of satellite measurements can result in a set ofpossible location estimates for the mobile device in the form of aregion or an area of possible location estimates. In the case of four ormore than four satellite measurements in a cluster, a cluster ofsatellite measurements can result in a location estimate for the mobiledevice. A cluster is defined as a set of measurements which point to asmall geographical area as a potential location for the mobile device. Asmall geographical area is defined based on nominal coverage of WLANAPs, and can be on the order of a couple of ten meters. In the case ofsatellite measurements, two satellites do not form a cluster. If weconsider only two satellite measurements, satellite equations are goingto be as follows:

r _(s1) =r ₁ +b

r _(s2) =r ₂ +b

In which r_(s) is the pseudorange measurement, r is the actual distancefrom satellite, and b is the clock bias of SPS receiver. The index oneand two are used for a first satellite and a second satellite. As it isseen in the above equations, there are three unknowns and two equations.Therefore, there is a set of solutions, or for any value of the clockbias of the SPS receiver there is a solution for r₁ and r₂. In the caseof two satellites, the consistency between the measurements cannot becalculated. Therefore, there is no cluster of only two satellites.However, if a location estimate from WLAN-PS is also considered, theexact distance of satellites to the estimated location of WLAN-PS can becalculated (r₁ and r₂), and the value of b can be found from bothequations. If the estimated location by WLAN-PS is correct, thesatellite measurements are correct, and the estimated location is theexact location of the mobile device; the calculated b from bothequations should be exactly the same. Otherwise, they are different, andthe difference between calculated b values from two equations is anindication of the distance between the estimated locations of theWLAN-PS and the satellite measurements. In other words, in the case thata cluster consists of two satellites and a location estimate fromWLAN-PS, the difference between b values is an indication of consistencyof the measurements.

In the case of three or more satellites, the consistency betweensatellite measurements can be calculated. For example, the equations aregoing to be as follows for three satellites measurements

r _(s1) =r ₁ +b

r _(s2) =r ₂ +b

r _(s3) =r ₃ +b

Assuming any value for clock bias of SPS receiver, b, results insolutions for r₁, r₂, and r₃, which are the distances between threesatellites, the end solution is the intersection of three spheres.Ideally, the three spheres intersect at one point, but if they do not,the distance between intersections is an indication of consistencybetween satellite measurements. The measurements which are consistentare considered as a cluster.

If the measurements from the WLAN-PS and SPS form more than one cluster,the clusters can be identified and the quality of each cluster can bedetermined. Then, the cluster with the best quality metric can beselected to be used to calculate the location of the mobile device.There are known methods to measure the quality of the SPS measurements,for example, Dilution of Precision (see Global Positioning System:Signals, Measurements and Performance by Pratap Misra and Per Enge(2006), the entire disclosure of which is herein incorporated byreference.). The quality of clusters can be calculated based on numberof WLAN APs in each cluster, the quality of measurements from the WLANAPs, the number of satellites, the consistency between satellitemeasurements and WLAN APs estimated location, and the quality ofsatellite measurements.

In various embodiments, the quality metric can be an aggregate of anumber WLAN APs and satellite measurements in a cluster, it can be thenumber of WLAN APs in the cluster with at least two satellites, or itcan be the WLAN-PS location estimate, which is then used to reject lowquality satellite measurements when more than four satellites areacquired. In this last embodiment, the best set of four satellites canthen be used to locate the mobile device. In another example, aftercollecting measurements from satellites and WLAN APs, in the first steponly WLAN APs are considered for clustering. Then all the satellitemeasurements are checked against the location estimate from each clusterof WLAN APs. From the satellite measurements, a subset is added to theassociated measurements of each cluster, which is consistent with theWLAN APs reported location.

The last step is selecting a cluster with the best quality in order toestimate the location of the mobile device. The measurements in thiscluster can be used to estimate the location of the mobile device. Anexample is shown in FIG. 5, in which signals from three satellites 503,504, 505 and WLAN APs 509 were acquired. WLAN-PS 501 results to alocation estimate 502. In this example, the WLAN APs 509 are close toeach other and form only one cluster, and three satellite 503, 504, 505measurements can be considered two at the time and in this case thereare three different sets of solutions 506, 507, 508. However, only oneof satellite solutions 506 includes the WLAN-PS location estimate 502.Therefore, the two satellites 503, 504 and the WLAN APs are consideredto estimate the location of the mobile device

Another embodiment provides a method and system to select the best setof SPS satellite measurements using the WLAN-PS results. If the numberof acquired satellites is more than the minimum of four satellitesrequired to calculate the location of the mobile device, the SPS canselect the best set of satellite measurements based on the satellitemeasurements' consistency with the WLAN-PS estimate location. The SPSsignal is subject to multipath in an indoor or urban environment, whichcan cause large error in measurements for some satellites. Therefore,the WLAN-PS estimation can be used as an initial estimate of the mobiledevice location and can be used as another criterion to accept or rejectsatellite measurements based on distance between the SPS locationestimate and the WLAN-PS estimated location. Therefore, the WLAN-PSestimated location and expected error also are two additional parameterswhich can be used to select the best set of satellite measurements toestimate the location of the mobile device using SPS.

A satellite measurement can be considered to be consistent with a WLANbased location estimate if the distance between location estimate fromthe set of satellite measurement and location estimate from WLAN APs isless than the expected error of WLAN-PS or SPS. The expected error ofthe WLAN-PS can be, for example, 10 to 500 meters and the expected errorof the SPS can be, for example, 1 to 500 meters. The nominal WLAN-PSerror can be, 30 to 40 meters, and the nominal error can be, forexample, 5 to 10 meters. In some embodiments, the distance between theWLAN based location estimate and the location estimate result from theset of satellite measurements can be measured to provide a measurementof the consistency of the satellite measurements and the WLAN basedposition estimate. For example, if the distance between the locationestimate result from the set of satellite measurement and the WLAN basedlocation estimate is far, for example, on the order of one hundredmeters, that satellite measurement can be considered to be inconsistentwith the WLAN based position estimate. Therefore, that satellite measurecan be eliminated from the position estimation calculation. If thedistance between the location estimate result from the set of satellitemeasurements and the WLAN based position estimate is small, for example,on the order of ten meters, those satellite measurements can bedetermined to be consistent with the WLAN based position estimate andthose satellite measurements can be used to estimate location of themobile device.

FIG. 6 illustrates an integrated WLAN-PS and SPS system, in which SPShas acquired five satellites 604, 605, 606, 607, and 608. It is shownthat using satellites 604, 605, 607 and 608 (a first cluster ofsatellites) results in location estimate 602, which is different thanlocation estimate 609, which was a result of using satellites 605, 606,607 and 608 (a second cluster of satellites). Because WLAN-PS 601estimated location area 603 is consistent with estimated location 602and not 609, the final location estimate of the mobile device isreported as 602, which is consistent with the first cluster ofsatellites. Further, because satellite 606 was the only satellite thatindicated the incorrect position, it can be identified as an erroneoussatellite measurement.

FIG. 7 illustrates an integrated WLAN-PS and SPS system, in which rawSPS measurements and WLAN APs are selected in an integrated fashion.

SPS 706 includes the same modules as conventional systems, except thatraw SPS measurements from all the satellites 712 are output to a newmodule, combined satellite and AP selection device 711, which selectsthe best set of raw SPS measurements and the combined satellite and APselection device 711 returns the selected set of raw SPS measurementsfor position estimation calculation back to trilateration device 208 inthe SPS 706. Off-the-shelf SPS receivers 306 usually do not providemechanisms to select raw SPS measurements outside the module. Therefore,the SPS receiver should be modified to accommodate these requirements.

WLAN-PS 701 consists of all the conventional modules, except selectionof WLAN APs. WLAN AP selection logic is modified and it is incorporatedwith raw SPS measurement 712 in combined satellite and AP selectiondevice 711, which is shown outside WLAN-PS 701 and SPS 706.

The combined satellite and AP selection device 711 receives a list ofdetected WLAN APs 713, and raw SPS measurements 712 and applies logic toselect the best set of raw SPS measurements and WLAN APs based onaggregate information provided by both systems. Logic can be a set ofcomputer readable instructions or software, stored on a computerreadable medium. The computer readable medium can be located in any ofthe devices, modules or systems disclosed herein. Moreover, the logicprocessing could be controlled by a software program on one or morecomputer systems or processors, or could even be partially or whollyimplemented in hardware.

A procedure is here, and generally, conceived to be a self-consistentsequence of steps leading to a desired result. These steps are thoserequiring physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared and otherwise manipulated. It proves convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers, or thelike. It should be noted, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities.

Further, the manipulations performed are often referred to in terms,such as adding or comparing, which are commonly associated with mentaloperations performed by a human operator. No such capability of a humanoperator is necessary, or desirable in most cases, in any of theoperations described herein which form part of the present disclosure;the operations are machine operations. Useful machines for performingthe operation of the present invention include general purpose digitalcomputers or similar devices.

The present invention also relates to apparatus for performing theseoperations. This apparatus may be specially constructed for the requiredpurpose or it may comprise a general purpose computer as selectivelyactivated or reconfigured by a computer program stored in the computer.The procedures presented herein are not inherently related to aparticular computer or other apparatus. Various general purpose machinesmay be used with programs written in accordance with the teachingsherein, or it may prove more convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these machines will appear from the descriptionprovided above.

Although a single computer may be used, the system according to one ormore embodiments of the invention is optionally suitably equipped with amultitude or combination of processors or storage devices. For example,the computer may be replaced by, or combined with, any suitableprocessing system operative in accordance with the concepts ofembodiments of the present invention, including sophisticatedcalculators, hand held, laptop/notebook, mini, mainframe and supercomputers, as well as processing system network combinations of thesame. Further, portions of the system may be provided in any appropriateelectronic format, including, for example, provided over a communicationline as electronic signals, provided on CD and/or DVD, provided onoptical disk memory, etc.

Any presently available or future developed computer software languageand/or hardware components can be employed in such embodiments of thepresent invention. For example, at least some of the functionalitymentioned above could be implemented using Visual Basic, C, C++ or anyassembly language appropriate in view of the processor being used. Itcould also be written in an object-oriented and/or interpretiveenvironment such as Java and transported to multiple destinations tovarious users.

It is to be understood that the invention is not limited in itsapplication to the details of construction and to the arrangements ofthe components set forth in the foregoing description or illustrated inthe drawings. Accordingly, it will be understood that the invention iscapable of other embodiments and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein are for the purpose of description andshould not be regarded as limiting.

Those skilled in the art will appreciate that the conception, upon whichthis disclosure is based, may readily be utilized as a basis for thedesigning of other structures, methods and systems for carrying out theseveral purposes of the present invention. It is important, therefore,that the claims be regarded as including such equivalent constructionsinsofar as they do not depart from the spirit and scope of the presentinvention.

The many features and advantages of the embodiments of the presentinvention are apparent from the detail specification, and thus, it isintended to cover all such features and advantages of the invention thatfall within the true spirit and scope of the invention. All suitablemodifications and equivalents maybe resorted to, falling within thescope of the invention.

1. A method of using a Wireless Local Area Network (WLAN) and satelliteenabled device to infer that a reference location associated with adetected WLAN access point (AP) is not the present location of the AP,the method comprising: identifying at least one WLAN AP detected by theWLAN and satellite enabled device; accessing a reference database toobtain a reference location associated with the at least one WLAN AP anda quality measurement associated with the reference location; receivinga position estimate for the device from a Satellite Positioning System(SPS); estimating a distance between the reference location associatedwith the WLAN AP and the position estimate of the device from the SPS;and inferring that the reference location associated with the WLAN AP isnot the present location of the WLAN AP based on (i) the distancebetween the reference location associated with the WLAN AP and theposition estimate of the device from the SPS and (ii) the qualitymeasurement associated with the reference location.
 2. The method ofclaim 1, further comprising indicating in the reference database thatthe reference location associated with the WLAN AP is not the presentlocation of the WLAN AP.
 3. The method of claim 1, further comprisingupdating the reference location associated with the WLAN AP in thereference database to reflect an estimated present location of theassociated WLAN AP.
 4. The method of claim 1, the inferring that thereference location associated with the WLAN AP is not the presentlocation of the WLAN AP being based on the distance between thereference location associated with the WLAN AP and the position estimateof the device from the SPS exceeding a predetermined threshold.
 5. Themethod of claim 4, wherein the predetermined threshold is based on anestimated coverage area of the WLAN AP.
 6. A system for using a WirelessLocal Area Network (WLAN) and satellite enabled device to infer that areference location associated with a detected WLAN access point (AP) isnot the present location of the AP, the system comprising: logic foridentifying at least one WLAN AP detected by the WLAN and satelliteenabled device; logic for accessing a reference database to obtain areference location associated with the at least one WLAN AP and aquality measurement associated with the reference location; logic forproviding a position estimate for the device from a SatellitePositioning System (SPS); logic for estimating a distance between thereference location associated with the WLAN AP and the position estimateof the device from the SPS; and logic for inferring that the referencelocation associated with the WLAN AP is not the present location of theWLAN AP based on (i) the distance between the reference locationassociated with the WLAN AP and the position estimate of the device fromthe SPS and (ii) the quality measurement associated with the referencelocation.
 7. The system of claim 6, further comprising logic forindicating in the reference database that the reference locationassociated with the WLAN AP is not the present location of the WLAN AP.8. The system of claim 6, further comprising logic for updating thereference location associated with the WLAN AP in the reference databaseto reflect an estimated present location of the associated WLAN AP. 9.The system of claim 6, the inferring that the reference locationassociated with the WLAN AP is not the present location of the WLAN APbeing based on the distance between the reference location associatedwith the WLAN AP and the position estimate of the device from the SPSexceeding a predetermined threshold.
 10. The system of claim 9, whereinthe predetermined threshold is based on an estimated coverage area ofthe WLAN AP.